The relationship of chemical structure to mutagenicity in Salmonella is being examined using data provided by the National Toxicology Program. The first set of compounds considered are the nitro-compounds and their homologs which do not contain a nitro- group. Examination of the structures of the nitro-compounds already tested and selected for testing aided in proposing 52 additional compounds for testing, about 60% of which were selected. Several treatments of the mutagenicity data have been developed to compare a broad spectrum of observed activities. Some of the findings can be summarized as follows. Primary nitroalkanes gave the lowest mutagenicity rates. The secondary nitroalkane, 2-nitropropane, however, yielded low but significant mutagenicity rates. Nitrobenzene was considered nonmutagenic. The trisubstituted, monocyclic aromatic compounds contained a greater number of compounds in the more mutagenic ranges than did the group of disubstituted derivatives. The sets of di- and trisubstituted compounds had the greatest numbers of representatives tested. With one exception, di- and trinitro-, tetrasubstituted monocyclic aromatic compounds were rather mutagenic. No mononitro-, tetrasubstituted derivatives have yet been tested. Some of the penta- and hexasubstituted compounds yielded the most variable data. As expected, some of the polycyclic aromatic and heterocyclic compounds were highly mutagenic. A homologous set of compounds that did not contain the nitro- group yielded mainly negative results or the compounds were weaker mutagens than their homologs. A review of the hazards of methanol in individuals through nineteen years-of-age has been completed.